Regiospecific syntheses of tritium labelled precocene I (5a) and precocene II (5b), the antijuvenile hormones, have been accomplished. The syntheses involved condensations between 2-hydroxyacetophenones (1) with acetone-T to give cross condensation products 2 which on cyclodehydration furnished 2,2-dimethyl-4-chromanones-(2-gem dimethyl-T) (3). Reduction of 3 with lithium aluminium hydride gave chroman-4-ols (2-gem dimethyl-T) (4). Dehydration of 4 furnished 2,2-dimethyl- chromenes- (2-gem dimethyl-T) (5). Starting with appropriate acetophenones and acetone-T, precocene I (7-methoxy-2,2-dimethylchromene) and precocene II (6, 7-dimethoxy-2, 2-dimethylchromene) labelled with tritium in the 2-gemdimethyl positions, have been synthesised in high chemical as well as radiochemical yields.
A. Banerji and Goomer, N. C., “Synthesis of tritium labelled precocenes”, Journal of Labelled Compounds and Radiopharmaceuticals, vol. 18, pp. 1737–1741, 1981.